I just did the cat nip gunner using trigger happy and the other 2 dark knights to heal, he tends physicaly attack first and then use genesis, if your gunner has haste you may luckily be able to use a second trigger happy which should finish him off.I had problems with him, sometimes i'd beat him sometimes not.
Trema is pretty easy, put protect on your dark knights (id advise using dark knights) and put mana springs at the top of your item list. Firstly use mana springs to drain his mp or he'll use Flare & Ultima. Then just use trigger happy and have the guards heal/revive when necessary. Watch out for Meteor, it requires no mp, and can do about 2000+ damage (depending on your defense levels) just heal and such, should be easy.
REMEMBER THERE IS NO EPISODE COMPLETE FOR BEATING VIA INFINITO!